It is well known that the aluminum content of a zeolite determines to a great extent its properties such as catalytic activity, sorption and ion-exchange capacity. It is also well known that the aluminum content of various zeolites can be decreased by various methods such as acid leaching, SiCl.sub.4 treatment, and hydrolysis. However, increasing the framework aluminum content of a freshly synthesized or a dealuminated zeolite has been a controversial issue [see D. C. Breck and G. W. Skeels, Proc. 5th Int. Conf. on Zeolites, p. 335(1980) and G. Englehardt and U. Lohse, J. Catal. 88, 513 (1984)] for the past several years and only recently have some techniques emerged. Recent literature reports claim that aluminum can be substituted for silicon in highly siliceous ZSM-5 by prolonged treatment with AlCl.sub.3 vapor or with alumina at elevated temperatures. [see C. D. Chang, et al., J. C. S. Faraday I, 81,2215 (1985) and M. W. Anderson, J. Klinowski and X. Liu, J. C. S. Chem. Comm., 1596(1984)].
The present invention provides a convenient and inexpensive method for increasing the framework aluminum content of either freshly synthesized or dealuminated zeolites.